It's easy for gardeners to social distance if only one gardener is allowed to work on a plot at a time. It is also easy to distinguish gardeners from casual socializrs. To reduce the impact of COVID-19 there are other places requiring PRIORITY attention, such as nursing homes where many who live in them cannot social isolate, even if they have the virus.
If we lose this growing season, a whole year of food will be lost (and mental and physical benefits of the entire gardening year). Food production is essential, whether on a commercial or individual scale, and the means of food production shouldn't be closed down. With social distancing protocols, there is no reason to forbid access to community gardens on public land.